The present invention relates to ramp-intersect digital firing control systems. Digital pulse generators are known to include a comparator which detects the desired firing angle in relation to a synthesized time dependent reference synchronized with one phase of AC lines upon which thyristors are connected for sequential firing. See for instance U.S. Pat. Nos. 4,173,722; 4,028,609 and 4,017,744.
The prior art shows the use of equidistant firing delay circuits as applied to power converters and motor drive controllers. Ramp-intersect is applied consisting in deriving, from one phase of the AC power lines, a representation of the electrical angles from zero-crossing to zero-crossing, and in comparing such "running-count" with a reference signal representing a desired firing angle for the respective static power switches.
The trend in power electronics being to use "all digital" control systems with a microprocessor facility, the prior art has implemented gate pulse genernators which are microprocessor-based.
The prior art has been deficient in at least two respects. The digital implementations have been unable to provide a rapid response of the digital pulse generator to sudden changes in the reference signal determining the firing angle. The present invention provides for such immediate response. Moreover, it is desirable in all "all digital" system to be able to maximize the use of large scale integrated (LSI) circuit techniques. This depends to a large degree upon an easy interface of the digital control system between the control inputs and the microprocessor. The present invention allows an LSI chip to be interfaced easily and directly to a reference voltage determining the firing angle in a ramp-intersect digital control system.
It is also desirable to use a picket-fence signal and a pulse suppressor, as well as to accommodate end-stop technique, typically as shown in the Detering U.S. Pat. Nos. 4,028,609 and 4,173,722.